/* TODO:
*
- * - The WATCH helper will be used to signal the cache system
- * we need to flush a given key/dbid into disk, adding this key/dbid
- * pair into a server.ds_cache_dirty linked list AND hash table (so that we
- * don't add the same thing multiple times).
+ * WARNING: most of the following todo items and design issues are no
+ * longer relevant with the new design. Here as a checklist to see if
+ * some old ideas still apply.
*
- * - cron() checks if there are elements on this list. When there are things
- * to flush, we create an IO Job for the I/O thread.
- * NOTE: We disalbe object sharing when server.ds_enabled == 1 so objects
- * that are referenced an IO job for flushing on disk are marked as
- * o->storage == REDIS_DS_SAVING.
+ * - What happens when an object is destroyed?
*
- * - This is what we do on key lookup:
- * 1) The key already exists in memory. object->storage == REDIS_DS_MEMORY
- * or it is object->storage == REDIS_DS_DIRTY:
- * We don't do nothing special, lookup, return value object pointer.
- * 2) The key is in memory but object->storage == REDIS_DS_SAVING.
- * When this happens we block waiting for the I/O thread to process
- * this object. Then continue.
- * 3) The key is not in memory. We block to load the key from disk.
- * Of course the key may not be present at all on the disk store as well,
- * in such case we just detect this condition and continue, returning
- * NULL from lookup.
+ * If the object is destroyed since semantically it was deleted or
+ * replaced with something new, we don't care if there was a SAVE
+ * job pending for it. Anyway when the IO JOb will be created we'll get
+ * the pointer of the current value.
*
- * - Preloading of needed keys:
- * 1) As it was done with VM, also with this new system we try preloading
- * keys a client is going to use. We block the client, load keys
- * using the I/O thread, unblock the client. Same code as VM more or less.
+ * If the object is already a REDIS_IO_SAVEINPROG object, then it is
+ * impossible that we get a decrRefCount() that will reach refcount of zero
+ * since the object is both in the dataset and in the io job entry.
*
- * - Reclaiming memory.
- * In cron() we detect our memory limit was reached. What we
- * do is deleting keys that are REDIS_DS_MEMORY, using LRU.
+ * - What happens with MULTI/EXEC?
*
- * If this is not enough to return again under the memory limits we also
- * start to flush keys that need to be synched on disk synchronously,
- * removing it from the memory. We do this blocking as memory limit is a
- * much "harder" barrirer in the new design.
+ * Good question. Without some kind of versioning with a global counter
+ * it is not possible to have trasactions on disk, but they are still
+ * useful since from the point of view of memory and client bugs it is
+ * a protection anyway. Also it's useful for WATCH.
*
- * - IO thread operations are no longer stopped for sync loading/saving of
- * things. When a key is found to be in the process of being saved
- * we simply wait for the IO thread to end its work.
+ * Btw there is to check what happens when WATCH gets combined to keys
+ * that gets removed from the object cache. Should be save but better
+ * to check.
*
- * Otherwise if there is to load a key without any IO thread operation
- * just started it is blocking-loaded in the lookup function.
+ * - Check if/why INCR will not update the LRU info for the object.
*
- * - What happens when an object is destroyed?
+ * - Fix/Check the following race condition: a key gets a DEL so there is
+ * a write operation scheduled against this key. Later the same key will
+ * be the argument of a GET, but the write operation was still not
+ * completed (to delete the file). If the GET will be for some reason
+ * a blocking loading (via lookup) we can load the old value on memory.
*
- * If o->storage == REDIS_DS_MEMORY then we simply destory the object.
- * If o->storage == REDIS_DS_DIRTY we can still remove the object. It had
- * changes not flushed on disk, but is being removed so
- * who cares.
- * if o->storage == REDIS_DS_SAVING then the object is being saved so
- * it is impossible that its refcount == 1, must be at
- * least two. When the object is saved the storage will
- * be set back to DS_MEMORY.
+ * This problems can be fixed with negative caching. We can use it
+ * to optimize the system, but also when a key is deleted we mark
+ * it as non existing on disk as well (in a way that this cache
+ * entry can't be evicted, setting time to 0), then we avoid looking at
+ * the disk at all if the key can't be there. When an IO Job complete
+ * a deletion, we set the time of the negative caching to a non zero
+ * value so it will be evicted later.
*
- * - What happens when keys are deleted?
+ * Are there other patterns like this where we load stale data?
*
- * We simply schedule a key flush operation as usually, but when the
- * IO thread will be created the object pointer will be set to NULL
- * so the IO thread will know that the work to do is to delete the key
- * from the disk store.
+ * Also, make sure that key preloading is ONLY done for keys that are
+ * not marked as cacheKeyDoesNotExist(), otherwise, again, we can load
+ * data from disk that should instead be deleted.
*
- * - What happens with MULTI/EXEC?
+ * - dsSet() should use rename(2) in order to avoid corruptions.
+ *
+ * - Don't add a LOAD if there is already a LOADINPROGRESS, or is this
+ * impossible since anyway the io_keys stuff will work as lock?
*
- * Good question.
+ * - Serialize special encoded things in a raw form.
+ *
+ * - When putting IO read operations on top of the queue, do this only if
+ * the already-on-top operation is not a save or if it is a save that
+ * is scheduled for later execution. If there is a save that is ready to
+ * fire, let's insert the load operation just before the first save that
+ * is scheduled for later exection for instance.
+ *
+ * - Support MULTI/EXEC transactions via a journal file, that is played on
+ * startup to check if there is cleanup to do. This way we can implement
+ * transactions with our simple file based KV store.
*/
/* Virtual Memory is composed mainly of two subsystems:
* as a fully non-blocking VM.
*/
-/* =================== Virtual Memory - Blocking Side ====================== */
+void spawnIOThread(void);
+int cacheScheduleIOPushJobs(int flags);
+int processActiveIOJobs(int max);
-/* Create a VM pointer object. This kind of objects are used in place of
- * values in the key -> value hash table, for swapped out objects. */
-vmpointer *createVmPointer(int vtype) {
- vmpointer *vp = zmalloc(sizeof(vmpointer));
-
- vp->type = REDIS_VMPOINTER;
- vp->storage = REDIS_VM_SWAPPED;
- vp->vtype = vtype;
- return vp;
-}
+/* =================== Virtual Memory - Blocking Side ====================== */
-void vmInit(void) {
- off_t totsize;
+void dsInit(void) {
int pipefds[2];
size_t stacksize;
- struct flock fl;
- if (server.vm_max_threads != 0)
- zmalloc_enable_thread_safeness(); /* we need thread safe zmalloc() */
+ zmalloc_enable_thread_safeness(); /* we need thread safe zmalloc() */
- redisLog(REDIS_NOTICE,"Using '%s' as swap file",server.vm_swap_file);
- /* Try to open the old swap file, otherwise create it */
- if ((server.vm_fp = fopen(server.vm_swap_file,"r+b")) == NULL) {
- server.vm_fp = fopen(server.vm_swap_file,"w+b");
- }
- if (server.vm_fp == NULL) {
- redisLog(REDIS_WARNING,
- "Can't open the swap file: %s. Exiting.",
- strerror(errno));
+ redisLog(REDIS_NOTICE,"Opening Disk Store: %s", server.ds_path);
+ /* Open Disk Store */
+ if (dsOpen() != REDIS_OK) {
+ redisLog(REDIS_WARNING,"Fatal error opening disk store. Exiting.");
exit(1);
- }
- server.vm_fd = fileno(server.vm_fp);
- /* Lock the swap file for writing, this is useful in order to avoid
- * another instance to use the same swap file for a config error. */
- fl.l_type = F_WRLCK;
- fl.l_whence = SEEK_SET;
- fl.l_start = fl.l_len = 0;
- if (fcntl(server.vm_fd,F_SETLK,&fl) == -1) {
- redisLog(REDIS_WARNING,
- "Can't lock the swap file at '%s': %s. Make sure it is not used by another Redis instance.", server.vm_swap_file, strerror(errno));
- exit(1);
- }
- /* Initialize */
- server.vm_next_page = 0;
- server.vm_near_pages = 0;
- server.vm_stats_used_pages = 0;
- server.vm_stats_swapped_objects = 0;
- server.vm_stats_swapouts = 0;
- server.vm_stats_swapins = 0;
- totsize = server.vm_pages*server.vm_page_size;
- redisLog(REDIS_NOTICE,"Allocating %lld bytes of swap file",totsize);
- if (ftruncate(server.vm_fd,totsize) == -1) {
- redisLog(REDIS_WARNING,"Can't ftruncate swap file: %s. Exiting.",
- strerror(errno));
- exit(1);
- } else {
- redisLog(REDIS_NOTICE,"Swap file allocated with success");
- }
- server.vm_bitmap = zcalloc((server.vm_pages+7)/8);
- redisLog(REDIS_VERBOSE,"Allocated %lld bytes page table for %lld pages",
- (long long) (server.vm_pages+7)/8, server.vm_pages);
+ };
- /* Initialize threaded I/O (used by Virtual Memory) */
+ /* Initialize threaded I/O for Object Cache */
server.io_newjobs = listCreate();
server.io_processing = listCreate();
server.io_processed = listCreate();
server.io_ready_clients = listCreate();
pthread_mutex_init(&server.io_mutex,NULL);
- pthread_mutex_init(&server.io_swapfile_mutex,NULL);
+ pthread_cond_init(&server.io_condvar,NULL);
+ pthread_mutex_init(&server.bgsavethread_mutex,NULL);
server.io_active_threads = 0;
if (pipe(pipefds) == -1) {
- redisLog(REDIS_WARNING,"Unable to intialized VM: pipe(2): %s. Exiting."
+ redisLog(REDIS_WARNING,"Unable to intialized DS: pipe(2): %s. Exiting."
,strerror(errno));
exit(1);
}
if (aeCreateFileEvent(server.el, server.io_ready_pipe_read, AE_READABLE,
vmThreadedIOCompletedJob, NULL) == AE_ERR)
oom("creating file event");
-}
-
-/* Mark the page as used */
-void vmMarkPageUsed(off_t page) {
- off_t byte = page/8;
- int bit = page&7;
- redisAssert(vmFreePage(page) == 1);
- server.vm_bitmap[byte] |= 1<<bit;
-}
-
-/* Mark N contiguous pages as used, with 'page' being the first. */
-void vmMarkPagesUsed(off_t page, off_t count) {
- off_t j;
-
- for (j = 0; j < count; j++)
- vmMarkPageUsed(page+j);
- server.vm_stats_used_pages += count;
- redisLog(REDIS_DEBUG,"Mark USED pages: %lld pages at %lld\n",
- (long long)count, (long long)page);
-}
-
-/* Mark the page as free */
-void vmMarkPageFree(off_t page) {
- off_t byte = page/8;
- int bit = page&7;
- redisAssert(vmFreePage(page) == 0);
- server.vm_bitmap[byte] &= ~(1<<bit);
-}
-
-/* Mark N contiguous pages as free, with 'page' being the first. */
-void vmMarkPagesFree(off_t page, off_t count) {
- off_t j;
-
- for (j = 0; j < count; j++)
- vmMarkPageFree(page+j);
- server.vm_stats_used_pages -= count;
- redisLog(REDIS_DEBUG,"Mark FREE pages: %lld pages at %lld\n",
- (long long)count, (long long)page);
-}
-
-/* Test if the page is free */
-int vmFreePage(off_t page) {
- off_t byte = page/8;
- int bit = page&7;
- return (server.vm_bitmap[byte] & (1<<bit)) == 0;
-}
-
-/* Find N contiguous free pages storing the first page of the cluster in *first.
- * Returns REDIS_OK if it was able to find N contiguous pages, otherwise
- * REDIS_ERR is returned.
- *
- * This function uses a simple algorithm: we try to allocate
- * REDIS_VM_MAX_NEAR_PAGES sequentially, when we reach this limit we start
- * again from the start of the swap file searching for free spaces.
- *
- * If it looks pretty clear that there are no free pages near our offset
- * we try to find less populated places doing a forward jump of
- * REDIS_VM_MAX_RANDOM_JUMP, then we start scanning again a few pages
- * without hurry, and then we jump again and so forth...
- *
- * This function can be improved using a free list to avoid to guess
- * too much, since we could collect data about freed pages.
- *
- * note: I implemented this function just after watching an episode of
- * Battlestar Galactica, where the hybrid was continuing to say "JUMP!"
- */
-int vmFindContiguousPages(off_t *first, off_t n) {
- off_t base, offset = 0, since_jump = 0, numfree = 0;
-
- if (server.vm_near_pages == REDIS_VM_MAX_NEAR_PAGES) {
- server.vm_near_pages = 0;
- server.vm_next_page = 0;
- }
- server.vm_near_pages++; /* Yet another try for pages near to the old ones */
- base = server.vm_next_page;
-
- while(offset < server.vm_pages) {
- off_t this = base+offset;
-
- /* If we overflow, restart from page zero */
- if (this >= server.vm_pages) {
- this -= server.vm_pages;
- if (this == 0) {
- /* Just overflowed, what we found on tail is no longer
- * interesting, as it's no longer contiguous. */
- numfree = 0;
- }
- }
- if (vmFreePage(this)) {
- /* This is a free page */
- numfree++;
- /* Already got N free pages? Return to the caller, with success */
- if (numfree == n) {
- *first = this-(n-1);
- server.vm_next_page = this+1;
- redisLog(REDIS_DEBUG, "FOUND CONTIGUOUS PAGES: %lld pages at %lld\n", (long long) n, (long long) *first);
- return REDIS_OK;
- }
- } else {
- /* The current one is not a free page */
- numfree = 0;
- }
-
- /* Fast-forward if the current page is not free and we already
- * searched enough near this place. */
- since_jump++;
- if (!numfree && since_jump >= REDIS_VM_MAX_RANDOM_JUMP/4) {
- offset += random() % REDIS_VM_MAX_RANDOM_JUMP;
- since_jump = 0;
- /* Note that even if we rewind after the jump, we are don't need
- * to make sure numfree is set to zero as we only jump *if* it
- * is set to zero. */
- } else {
- /* Otherwise just check the next page */
- offset++;
- }
- }
- return REDIS_ERR;
-}
-
-/* Write the specified object at the specified page of the swap file */
-int vmWriteObjectOnSwap(robj *o, off_t page) {
- if (server.vm_enabled) pthread_mutex_lock(&server.io_swapfile_mutex);
- if (fseeko(server.vm_fp,page*server.vm_page_size,SEEK_SET) == -1) {
- if (server.vm_enabled) pthread_mutex_unlock(&server.io_swapfile_mutex);
- redisLog(REDIS_WARNING,
- "Critical VM problem in vmWriteObjectOnSwap(): can't seek: %s",
- strerror(errno));
- return REDIS_ERR;
- }
- rdbSaveObject(server.vm_fp,o);
- fflush(server.vm_fp);
- if (server.vm_enabled) pthread_mutex_unlock(&server.io_swapfile_mutex);
- return REDIS_OK;
-}
-
-/* Transfers the 'val' object to disk. Store all the information
- * a 'vmpointer' object containing all the information needed to load the
- * object back later is returned.
- *
- * If we can't find enough contiguous empty pages to swap the object on disk
- * NULL is returned. */
-vmpointer *vmSwapObjectBlocking(robj *val) {
- off_t pages = rdbSavedObjectPages(val);
- off_t page;
- vmpointer *vp;
-
- redisAssert(val->storage == REDIS_VM_MEMORY);
- redisAssert(val->refcount == 1);
- if (vmFindContiguousPages(&page,pages) == REDIS_ERR) return NULL;
- if (vmWriteObjectOnSwap(val,page) == REDIS_ERR) return NULL;
-
- vp = createVmPointer(val->type);
- vp->page = page;
- vp->usedpages = pages;
- decrRefCount(val); /* Deallocate the object from memory. */
- vmMarkPagesUsed(page,pages);
- redisLog(REDIS_DEBUG,"VM: object %p swapped out at %lld (%lld pages)",
- (void*) val,
- (unsigned long long) page, (unsigned long long) pages);
- server.vm_stats_swapped_objects++;
- server.vm_stats_swapouts++;
- return vp;
-}
-
-robj *vmReadObjectFromSwap(off_t page, int type) {
- robj *o;
-
- if (server.vm_enabled) pthread_mutex_lock(&server.io_swapfile_mutex);
- if (fseeko(server.vm_fp,page*server.vm_page_size,SEEK_SET) == -1) {
- redisLog(REDIS_WARNING,
- "Unrecoverable VM problem in vmReadObjectFromSwap(): can't seek: %s",
- strerror(errno));
- _exit(1);
- }
- o = rdbLoadObject(type,server.vm_fp);
- if (o == NULL) {
- redisLog(REDIS_WARNING, "Unrecoverable VM problem in vmReadObjectFromSwap(): can't load object from swap file: %s", strerror(errno));
- _exit(1);
- }
- if (server.vm_enabled) pthread_mutex_unlock(&server.io_swapfile_mutex);
- return o;
-}
-
-/* Load the specified object from swap to memory.
- * The newly allocated object is returned.
- *
- * If preview is true the unserialized object is returned to the caller but
- * the pages are not marked as freed, nor the vp object is freed. */
-robj *vmGenericLoadObject(vmpointer *vp, int preview) {
- robj *val;
-
- redisAssert(vp->type == REDIS_VMPOINTER &&
- (vp->storage == REDIS_VM_SWAPPED || vp->storage == REDIS_VM_LOADING));
- val = vmReadObjectFromSwap(vp->page,vp->vtype);
- if (!preview) {
- redisLog(REDIS_DEBUG, "VM: object %p loaded from disk", (void*)vp);
- vmMarkPagesFree(vp->page,vp->usedpages);
- zfree(vp);
- server.vm_stats_swapped_objects--;
- } else {
- redisLog(REDIS_DEBUG, "VM: object %p previewed from disk", (void*)vp);
- }
- server.vm_stats_swapins++;
- return val;
-}
-/* Plain object loading, from swap to memory.
- *
- * 'o' is actually a redisVmPointer structure that will be freed by the call.
- * The return value is the loaded object. */
-robj *vmLoadObject(robj *o) {
- /* If we are loading the object in background, stop it, we
- * need to load this object synchronously ASAP. */
- if (o->storage == REDIS_VM_LOADING)
- vmCancelThreadedIOJob(o);
- return vmGenericLoadObject((vmpointer*)o,0);
-}
-
-/* Just load the value on disk, without to modify the key.
- * This is useful when we want to perform some operation on the value
- * without to really bring it from swap to memory, like while saving the
- * dataset or rewriting the append only log. */
-robj *vmPreviewObject(robj *o) {
- return vmGenericLoadObject((vmpointer*)o,1);
+ /* Spawn our I/O thread */
+ spawnIOThread();
}
-/* How a good candidate is this object for swapping?
- * The better candidate it is, the greater the returned value.
- *
- * Currently we try to perform a fast estimation of the object size in
- * memory, and combine it with aging informations.
- *
- * Basically swappability = idle-time * log(estimated size)
- *
- * Bigger objects are preferred over smaller objects, but not
- * proportionally, this is why we use the logarithm. This algorithm is
- * just a first try and will probably be tuned later. */
+/* Compute how good candidate the specified object is for eviction.
+ * An higher number means a better candidate. */
double computeObjectSwappability(robj *o) {
/* actual age can be >= minage, but not < minage. As we use wrapping
* 21 bit clocks with minutes resolution for the LRU. */
- time_t minage = estimateObjectIdleTime(o);
- long asize = 0, elesize;
- robj *ele;
- list *l;
- listNode *ln;
- dict *d;
- struct dictEntry *de;
- int z;
-
- if (minage <= 0) return 0;
- switch(o->type) {
- case REDIS_STRING:
- if (o->encoding != REDIS_ENCODING_RAW) {
- asize = sizeof(*o);
- } else {
- asize = sdslen(o->ptr)+sizeof(*o)+sizeof(long)*2;
- }
- break;
- case REDIS_LIST:
- if (o->encoding == REDIS_ENCODING_ZIPLIST) {
- asize = sizeof(*o)+ziplistSize(o->ptr);
- } else {
- l = o->ptr;
- ln = listFirst(l);
- asize = sizeof(list);
- if (ln) {
- ele = ln->value;
- elesize = (ele->encoding == REDIS_ENCODING_RAW) ?
- (sizeof(*o)+sdslen(ele->ptr)) : sizeof(*o);
- asize += (sizeof(listNode)+elesize)*listLength(l);
- }
- }
- break;
- case REDIS_SET:
- case REDIS_ZSET:
- z = (o->type == REDIS_ZSET);
- d = z ? ((zset*)o->ptr)->dict : o->ptr;
-
- if (!z && o->encoding == REDIS_ENCODING_INTSET) {
- intset *is = o->ptr;
- asize = sizeof(*is)+is->encoding*is->length;
- } else {
- asize = sizeof(dict)+(sizeof(struct dictEntry*)*dictSlots(d));
- if (z) asize += sizeof(zset)-sizeof(dict);
- if (dictSize(d)) {
- de = dictGetRandomKey(d);
- ele = dictGetEntryKey(de);
- elesize = (ele->encoding == REDIS_ENCODING_RAW) ?
- (sizeof(*o)+sdslen(ele->ptr)) : sizeof(*o);
- asize += (sizeof(struct dictEntry)+elesize)*dictSize(d);
- if (z) asize += sizeof(zskiplistNode)*dictSize(d);
- }
- }
- break;
- case REDIS_HASH:
- if (o->encoding == REDIS_ENCODING_ZIPMAP) {
- unsigned char *p = zipmapRewind((unsigned char*)o->ptr);
- unsigned int len = zipmapLen((unsigned char*)o->ptr);
- unsigned int klen, vlen;
- unsigned char *key, *val;
-
- if ((p = zipmapNext(p,&key,&klen,&val,&vlen)) == NULL) {
- klen = 0;
- vlen = 0;
- }
- asize = len*(klen+vlen+3);
- } else if (o->encoding == REDIS_ENCODING_HT) {
- d = o->ptr;
- asize = sizeof(dict)+(sizeof(struct dictEntry*)*dictSlots(d));
- if (dictSize(d)) {
- de = dictGetRandomKey(d);
- ele = dictGetEntryKey(de);
- elesize = (ele->encoding == REDIS_ENCODING_RAW) ?
- (sizeof(*o)+sdslen(ele->ptr)) : sizeof(*o);
- ele = dictGetEntryVal(de);
- elesize = (ele->encoding == REDIS_ENCODING_RAW) ?
- (sizeof(*o)+sdslen(ele->ptr)) : sizeof(*o);
- asize += (sizeof(struct dictEntry)+elesize)*dictSize(d);
- }
- }
- break;
- }
- return (double)minage*log(1+asize);
+ return (double) estimateObjectIdleTime(o);
}
-/* Try to swap an object that's a good candidate for swapping.
- * Returns REDIS_OK if the object was swapped, REDIS_ERR if it's not possible
- * to swap any object at all.
- *
- * If 'usethreaded' is true, Redis will try to swap the object in background
- * using I/O threads. */
-int vmSwapOneObject(int usethreads) {
+/* Try to free one entry from the diskstore object cache */
+int cacheFreeOneEntry(void) {
int j, i;
struct dictEntry *best = NULL;
double best_swappability = 0;
* are swappable objects */
int maxtries = 100;
- if (dictSize(db->dict) == 0) continue;
- for (i = 0; i < 5; i++) {
+ for (i = 0; i < 5 && dictSize(db->dict); i++) {
dictEntry *de;
double swappability;
+ robj keyobj;
+ sds keystr;
if (maxtries) maxtries--;
de = dictGetRandomKey(db->dict);
+ keystr = dictGetEntryKey(de);
val = dictGetEntryVal(de);
- /* Only swap objects that are currently in memory.
- *
- * Also don't swap shared objects: not a good idea in general and
- * we need to ensure that the main thread does not touch the
- * object while the I/O thread is using it, but we can't
- * control other keys without adding additional mutex. */
- if (val->storage != REDIS_VM_MEMORY || val->refcount != 1) {
+ initStaticStringObject(keyobj,keystr);
+
+ /* Don't remove objects that are currently target of a
+ * read or write operation. */
+ if (cacheScheduleIOGetFlags(db,&keyobj) != 0) {
if (maxtries) i--; /* don't count this try */
continue;
}
}
}
}
- if (best == NULL) return REDIS_ERR;
+ if (best == NULL) {
+ /* Not able to free a single object? we should check if our
+ * IO queues have stuff in queue, and try to consume the queue
+ * otherwise we'll use an infinite amount of memory if changes to
+ * the dataset are faster than I/O */
+ if (listLength(server.cache_io_queue) > 0) {
+ redisLog(REDIS_DEBUG,"--- Busy waiting IO to reclaim memory");
+ cacheScheduleIOPushJobs(REDIS_IO_ASAP);
+ processActiveIOJobs(1);
+ return REDIS_OK;
+ }
+ /* Nothing to free at all... */
+ return REDIS_ERR;
+ }
key = dictGetEntryKey(best);
val = dictGetEntryVal(best);
- redisLog(REDIS_DEBUG,"Key with best swappability: %s, %f",
+ redisLog(REDIS_DEBUG,"Key selected for cache eviction: %s swappability:%f",
key, best_swappability);
- /* Swap it */
- if (usethreads) {
- robj *keyobj = createStringObject(key,sdslen(key));
- vmSwapObjectThreaded(keyobj,val,best_db);
- decrRefCount(keyobj);
- return REDIS_OK;
- } else {
- vmpointer *vp;
-
- if ((vp = vmSwapObjectBlocking(val)) != NULL) {
- dictGetEntryVal(best) = vp;
- return REDIS_OK;
- } else {
- return REDIS_ERR;
- }
+ /* Delete this key from memory */
+ {
+ robj *kobj = createStringObject(key,sdslen(key));
+ dbDelete(best_db,kobj);
+ decrRefCount(kobj);
}
-}
-
-int vmSwapOneObjectBlocking() {
- return vmSwapOneObject(0);
-}
-
-int vmSwapOneObjectThreaded() {
- return vmSwapOneObject(1);
+ return REDIS_OK;
}
/* Return true if it's safe to swap out objects in a given moment.
* Basically we don't want to swap objects out while there is a BGSAVE
* or a BGAEOREWRITE running in backgroud. */
-int vmCanSwapOut(void) {
+int dsCanTouchDiskStore(void) {
return (server.bgsavechildpid == -1 && server.bgrewritechildpid == -1);
}
-/* =================== Virtual Memory - Threaded I/O ======================= */
+/* ==================== Disk store negative caching ========================
+ *
+ * When disk store is enabled, we need negative caching, that is, to remember
+ * keys that are for sure *not* on the disk key-value store.
+ *
+ * This is usefuls because without negative caching cache misses will cost us
+ * a disk lookup, even if the same non existing key is accessed again and again.
+ *
+ * With negative caching we remember that the key is not on disk, so if it's
+ * not in memory and we have a negative cache entry, we don't try a disk
+ * access at all.
+ */
+
+/* Returns true if the specified key may exists on disk, that is, we don't
+ * have an entry in our negative cache for this key */
+int cacheKeyMayExist(redisDb *db, robj *key) {
+ return dictFind(db->io_negcache,key) == NULL;
+}
+
+/* Set the specified key as an entry that may possibily exist on disk, that is,
+ * remove the negative cache entry for this key if any. */
+void cacheSetKeyMayExist(redisDb *db, robj *key) {
+ dictDelete(db->io_negcache,key);
+}
-void freeIOJob(iojob *j) {
- if ((j->type == REDIS_IOJOB_PREPARE_SWAP ||
- j->type == REDIS_IOJOB_DO_SWAP ||
- j->type == REDIS_IOJOB_LOAD) && j->val != NULL)
- {
- /* we fix the storage type, otherwise decrRefCount() will try to
- * kill the I/O thread Job (that does no longer exists). */
- if (j->val->storage == REDIS_VM_SWAPPING)
- j->val->storage = REDIS_VM_MEMORY;
- decrRefCount(j->val);
+/* Set the specified key as non existing on disk, that is, create a negative
+ * cache entry for this key. */
+void cacheSetKeyDoesNotExist(redisDb *db, robj *key) {
+ if (dictReplace(db->io_negcache,key,(void*)time(NULL))) {
+ incrRefCount(key);
+ }
+}
+
+/* Remove one entry from negative cache using approximated LRU. */
+int negativeCacheEvictOneEntry(void) {
+ struct dictEntry *de;
+ robj *best = NULL;
+ redisDb *best_db = NULL;
+ time_t time, best_time = 0;
+ int j;
+
+ for (j = 0; j < server.dbnum; j++) {
+ redisDb *db = server.db+j;
+ int i;
+
+ if (dictSize(db->io_negcache) == 0) continue;
+ for (i = 0; i < 3; i++) {
+ de = dictGetRandomKey(db->io_negcache);
+ time = (time_t) dictGetEntryVal(de);
+
+ if (best == NULL || time < best_time) {
+ best = dictGetEntryKey(de);
+ best_db = db;
+ best_time = time;
+ }
+ }
+ }
+ if (best) {
+ dictDelete(best_db->io_negcache,best);
+ return REDIS_OK;
+ } else {
+ return REDIS_ERR;
}
+}
+
+/* ================== Disk store cache - Threaded I/O ====================== */
+
+void freeIOJob(iojob *j) {
decrRefCount(j->key);
+ /* j->val can be NULL if the job is about deleting the key from disk. */
+ if (j->val) decrRefCount(j->val);
zfree(j);
}
* of an unix pipe in order to "awake" the main thread, and this function
* is called.
*
- * Note that this is called both by the event loop, when a I/O thread
- * sends a byte in the notification pipe, and is also directly called from
- * waitEmptyIOJobsQueue().
- *
- * In the latter case we don't want to swap more, so we use the
- * "privdata" argument setting it to a not NULL value to signal this
- * condition. */
+ * If privdata == NULL the function will try to put more jobs in the queue
+ * of IO jobs to process as more room is made. privdata is equal to NULL
+ * when the function is called from the event loop, so we want to push
+ * more IO jobs in the queue. Instead when the function is called by
+ * other functions that want to create a write-barrier to avoid race
+ * conditions we don't push new jobs in the queue. */
void vmThreadedIOCompletedJob(aeEventLoop *el, int fd, void *privdata,
int mask)
{
char buf[1];
- int retval, processed = 0, toprocess = -1, trytoswap = 1;
+ int retval, processed = 0, toprocess = -1;
REDIS_NOTUSED(el);
REDIS_NOTUSED(mask);
- REDIS_NOTUSED(privdata);
-
- if (privdata != NULL) trytoswap = 0; /* check the comments above... */
/* For every byte we read in the read side of the pipe, there is one
* I/O job completed to process. */
while((retval = read(fd,buf,1)) == 1) {
iojob *j;
listNode *ln;
- struct dictEntry *de;
redisLog(REDIS_DEBUG,"Processing I/O completed job");
j = ln->value;
listDelNode(server.io_processed,ln);
unlockThreadedIO();
- /* If this job is marked as canceled, just ignore it */
- if (j->canceled) {
- freeIOJob(j);
- continue;
- }
+
/* Post process it in the main thread, as there are things we
* can do just here to avoid race conditions and/or invasive locks */
- redisLog(REDIS_DEBUG,"COMPLETED Job type: %d, ID %p, key: %s", j->type, (void*)j->id, (unsigned char*)j->key->ptr);
- de = dictFind(j->db->dict,j->key->ptr);
- redisAssert(de != NULL);
+ redisLog(REDIS_DEBUG,"COMPLETED Job type %s, key: %s",
+ (j->type == REDIS_IOJOB_LOAD) ? "load" : "save",
+ (unsigned char*)j->key->ptr);
if (j->type == REDIS_IOJOB_LOAD) {
- redisDb *db;
- vmpointer *vp = dictGetEntryVal(de);
-
- /* Key loaded, bring it at home */
- vmMarkPagesFree(vp->page,vp->usedpages);
- redisLog(REDIS_DEBUG, "VM: object %s loaded from disk (threaded)",
- (unsigned char*) j->key->ptr);
- server.vm_stats_swapped_objects--;
- server.vm_stats_swapins++;
- dictGetEntryVal(de) = j->val;
- incrRefCount(j->val);
- db = j->db;
- /* Handle clients waiting for this key to be loaded. */
- handleClientsBlockedOnSwappedKey(db,j->key);
- freeIOJob(j);
- zfree(vp);
- } else if (j->type == REDIS_IOJOB_PREPARE_SWAP) {
- /* Now we know the amount of pages required to swap this object.
- * Let's find some space for it, and queue this task again
- * rebranded as REDIS_IOJOB_DO_SWAP. */
- if (!vmCanSwapOut() ||
- vmFindContiguousPages(&j->page,j->pages) == REDIS_ERR)
- {
- /* Ooops... no space or we can't swap as there is
- * a fork()ed Redis trying to save stuff on disk. */
- j->val->storage = REDIS_VM_MEMORY; /* undo operation */
- freeIOJob(j);
+ /* Create the key-value pair in the in-memory database */
+ if (j->val != NULL) {
+ /* Note: it's possible that the key is already in memory
+ * due to a blocking load operation. */
+ if (dbAdd(j->db,j->key,j->val) == REDIS_OK) {
+ incrRefCount(j->val);
+ if (j->expire != -1) setExpire(j->db,j->key,j->expire);
+ }
} else {
- /* Note that we need to mark this pages as used now,
- * if the job will be canceled, we'll mark them as freed
- * again. */
- vmMarkPagesUsed(j->page,j->pages);
- j->type = REDIS_IOJOB_DO_SWAP;
- lockThreadedIO();
- queueIOJob(j);
- unlockThreadedIO();
- }
- } else if (j->type == REDIS_IOJOB_DO_SWAP) {
- vmpointer *vp;
-
- /* Key swapped. We can finally free some memory. */
- if (j->val->storage != REDIS_VM_SWAPPING) {
- vmpointer *vp = (vmpointer*) j->id;
- printf("storage: %d\n",vp->storage);
- printf("key->name: %s\n",(char*)j->key->ptr);
- printf("val: %p\n",(void*)j->val);
- printf("val->type: %d\n",j->val->type);
- printf("val->ptr: %s\n",(char*)j->val->ptr);
- }
- redisAssert(j->val->storage == REDIS_VM_SWAPPING);
- vp = createVmPointer(j->val->type);
- vp->page = j->page;
- vp->usedpages = j->pages;
- dictGetEntryVal(de) = vp;
- /* Fix the storage otherwise decrRefCount will attempt to
- * remove the associated I/O job */
- j->val->storage = REDIS_VM_MEMORY;
- decrRefCount(j->val);
- redisLog(REDIS_DEBUG,
- "VM: object %s swapped out at %lld (%lld pages) (threaded)",
- (unsigned char*) j->key->ptr,
- (unsigned long long) j->page, (unsigned long long) j->pages);
- server.vm_stats_swapped_objects++;
- server.vm_stats_swapouts++;
- freeIOJob(j);
- /* Put a few more swap requests in queue if we are still
- * out of memory */
- if (trytoswap && vmCanSwapOut() &&
- zmalloc_used_memory() > server.vm_max_memory)
- {
- int more = 1;
- while(more) {
- lockThreadedIO();
- more = listLength(server.io_newjobs) <
- (unsigned) server.vm_max_threads;
- unlockThreadedIO();
- /* Don't waste CPU time if swappable objects are rare. */
- if (vmSwapOneObjectThreaded() == REDIS_ERR) {
- trytoswap = 0;
- break;
- }
+ /* Key not found on disk. If it is also not in memory
+ * as a cached object, nor there is a job writing it
+ * in background, we are sure the key does not exist
+ * currently.
+ *
+ * So we set a negative cache entry avoiding that the
+ * resumed client will block load what does not exist... */
+ if (dictFind(j->db->dict,j->key->ptr) == NULL &&
+ (cacheScheduleIOGetFlags(j->db,j->key) &
+ (REDIS_IO_SAVE|REDIS_IO_SAVEINPROG)) == 0)
+ {
+ cacheSetKeyDoesNotExist(j->db,j->key);
}
}
+ cacheScheduleIODelFlag(j->db,j->key,REDIS_IO_LOADINPROG);
+ handleClientsBlockedOnSwappedKey(j->db,j->key);
+ freeIOJob(j);
+ } else if (j->type == REDIS_IOJOB_SAVE) {
+ cacheScheduleIODelFlag(j->db,j->key,REDIS_IO_SAVEINPROG);
+ freeIOJob(j);
}
processed++;
+ if (privdata == NULL) cacheScheduleIOPushJobs(0);
if (processed == toprocess) return;
}
if (retval < 0 && errno != EAGAIN) {
pthread_mutex_unlock(&server.io_mutex);
}
-/* Remove the specified object from the threaded I/O queue if still not
- * processed, otherwise make sure to flag it as canceled. */
-void vmCancelThreadedIOJob(robj *o) {
- list *lists[3] = {
- server.io_newjobs, /* 0 */
- server.io_processing, /* 1 */
- server.io_processed /* 2 */
- };
- int i;
-
- redisAssert(o->storage == REDIS_VM_LOADING || o->storage == REDIS_VM_SWAPPING);
-again:
- lockThreadedIO();
- /* Search for a matching object in one of the queues */
- for (i = 0; i < 3; i++) {
- listNode *ln;
- listIter li;
-
- listRewind(lists[i],&li);
- while ((ln = listNext(&li)) != NULL) {
- iojob *job = ln->value;
-
- if (job->canceled) continue; /* Skip this, already canceled. */
- if (job->id == o) {
- redisLog(REDIS_DEBUG,"*** CANCELED %p (key %s) (type %d) (LIST ID %d)\n",
- (void*)job, (char*)job->key->ptr, job->type, i);
- /* Mark the pages as free since the swap didn't happened
- * or happened but is now discarded. */
- if (i != 1 && job->type == REDIS_IOJOB_DO_SWAP)
- vmMarkPagesFree(job->page,job->pages);
- /* Cancel the job. It depends on the list the job is
- * living in. */
- switch(i) {
- case 0: /* io_newjobs */
- /* If the job was yet not processed the best thing to do
- * is to remove it from the queue at all */
- freeIOJob(job);
- listDelNode(lists[i],ln);
- break;
- case 1: /* io_processing */
- /* Oh Shi- the thread is messing with the Job:
- *
- * Probably it's accessing the object if this is a
- * PREPARE_SWAP or DO_SWAP job.
- * If it's a LOAD job it may be reading from disk and
- * if we don't wait for the job to terminate before to
- * cancel it, maybe in a few microseconds data can be
- * corrupted in this pages. So the short story is:
- *
- * Better to wait for the job to move into the
- * next queue (processed)... */
-
- /* We try again and again until the job is completed. */
- unlockThreadedIO();
- /* But let's wait some time for the I/O thread
- * to finish with this job. After all this condition
- * should be very rare. */
- usleep(1);
- goto again;
- case 2: /* io_processed */
- /* The job was already processed, that's easy...
- * just mark it as canceled so that we'll ignore it
- * when processing completed jobs. */
- job->canceled = 1;
- break;
- }
- /* Finally we have to adjust the storage type of the object
- * in order to "UNDO" the operaiton. */
- if (o->storage == REDIS_VM_LOADING)
- o->storage = REDIS_VM_SWAPPED;
- else if (o->storage == REDIS_VM_SWAPPING)
- o->storage = REDIS_VM_MEMORY;
- unlockThreadedIO();
- redisLog(REDIS_DEBUG,"*** DONE");
- return;
- }
- }
- }
- unlockThreadedIO();
- printf("Not found: %p\n", (void*)o);
- redisAssert(1 != 1); /* We should never reach this */
-}
-
void *IOThreadEntryPoint(void *arg) {
iojob *j;
listNode *ln;
REDIS_NOTUSED(arg);
+ long long start;
pthread_detach(pthread_self());
+ lockThreadedIO();
while(1) {
/* Get a new job to process */
- lockThreadedIO();
if (listLength(server.io_newjobs) == 0) {
- /* No new jobs in queue, exit. */
- redisLog(REDIS_DEBUG,"Thread %ld exiting, nothing to do",
- (long) pthread_self());
- server.io_active_threads--;
- unlockThreadedIO();
- return NULL;
+ /* Wait for more work to do */
+ redisLog(REDIS_DEBUG,"[T] wait for signal");
+ pthread_cond_wait(&server.io_condvar,&server.io_mutex);
+ redisLog(REDIS_DEBUG,"[T] signal received");
+ continue;
}
+ start = ustime();
+ redisLog(REDIS_DEBUG,"[T] %ld IO jobs to process",
+ listLength(server.io_newjobs));
ln = listFirst(server.io_newjobs);
j = ln->value;
listDelNode(server.io_newjobs,ln);
/* Add the job in the processing queue */
- j->thread = pthread_self();
listAddNodeTail(server.io_processing,j);
ln = listLast(server.io_processing); /* We use ln later to remove it */
unlockThreadedIO();
- redisLog(REDIS_DEBUG,"Thread %ld got a new job (type %d): %p about key '%s'",
- (long) pthread_self(), j->type, (void*)j, (char*)j->key->ptr);
+
+ redisLog(REDIS_DEBUG,"[T] %ld: new job type %s: %p about key '%s'",
+ (long) pthread_self(),
+ (j->type == REDIS_IOJOB_LOAD) ? "load" : "save",
+ (void*)j, (char*)j->key->ptr);
/* Process the Job */
if (j->type == REDIS_IOJOB_LOAD) {
- vmpointer *vp = (vmpointer*)j->id;
- j->val = vmReadObjectFromSwap(j->page,vp->vtype);
- } else if (j->type == REDIS_IOJOB_PREPARE_SWAP) {
- j->pages = rdbSavedObjectPages(j->val);
- } else if (j->type == REDIS_IOJOB_DO_SWAP) {
- if (vmWriteObjectOnSwap(j->val,j->page) == REDIS_ERR)
- j->canceled = 1;
+ time_t expire;
+
+ j->val = dsGet(j->db,j->key,&expire);
+ if (j->val) j->expire = expire;
+ } else if (j->type == REDIS_IOJOB_SAVE) {
+ if (j->val) {
+ dsSet(j->db,j->key,j->val,j->expire);
+ } else {
+ dsDel(j->db,j->key);
+ }
}
/* Done: insert the job into the processed queue */
- redisLog(REDIS_DEBUG,"Thread %ld completed the job: %p (key %s)",
+ redisLog(REDIS_DEBUG,"[T] %ld completed the job: %p (key %s)",
(long) pthread_self(), (void*)j, (char*)j->key->ptr);
+
+ redisLog(REDIS_DEBUG,"[T] lock IO");
lockThreadedIO();
+ redisLog(REDIS_DEBUG,"[T] IO locked");
listDelNode(server.io_processing,ln);
listAddNodeTail(server.io_processed,j);
- unlockThreadedIO();
/* Signal the main thread there is new stuff to process */
redisAssert(write(server.io_ready_pipe_write,"x",1) == 1);
+ redisLog(REDIS_DEBUG,"TIME (%c): %lld\n", j->type == REDIS_IOJOB_LOAD ? 'L' : 'S', ustime()-start);
}
- return NULL; /* never reached */
+ /* never reached, but that's the full pattern... */
+ unlockThreadedIO();
+ return NULL;
}
void spawnIOThread(void) {
server.io_active_threads++;
}
-/* We need to wait for the last thread to exit before we are able to
- * fork() in order to BGSAVE or BGREWRITEAOF. */
-void waitEmptyIOJobsQueue(void) {
- while(1) {
+/* Wait that up to 'max' pending IO Jobs are processed by the I/O thread.
+ * From our point of view an IO job processed means that the count of
+ * server.io_processed must increase by one.
+ *
+ * If max is -1, all the pending IO jobs will be processed.
+ *
+ * Returns the number of IO jobs processed.
+ *
+ * NOTE: while this may appear like a busy loop, we are actually blocked
+ * by IO since we continuously acquire/release the IO lock. */
+int processActiveIOJobs(int max) {
+ int processed = 0;
+
+ while(max == -1 || max > 0) {
int io_processed_len;
+ redisLog(REDIS_DEBUG,"[P] lock IO");
lockThreadedIO();
+ redisLog(REDIS_DEBUG,"Waiting IO jobs processing: new:%d proessing:%d processed:%d",listLength(server.io_newjobs),listLength(server.io_processing),listLength(server.io_processed));
+
if (listLength(server.io_newjobs) == 0 &&
- listLength(server.io_processing) == 0 &&
- server.io_active_threads == 0)
+ listLength(server.io_processing) == 0)
{
+ /* There is nothing more to process */
+ redisLog(REDIS_DEBUG,"[P] Nothing to process, unlock IO, return");
unlockThreadedIO();
- return;
+ break;
}
- /* While waiting for empty jobs queue condition we post-process some
- * finshed job, as I/O threads may be hanging trying to write against
- * the io_ready_pipe_write FD but there are so much pending jobs that
- * it's blocking. */
+
+#if 1
+ /* If there are new jobs we need to signal the thread to
+ * process the next one. FIXME: drop this if useless. */
+ redisLog(REDIS_DEBUG,"[P] waitEmptyIOJobsQueue: new %d, processing %d, processed %d",
+ listLength(server.io_newjobs),
+ listLength(server.io_processing),
+ listLength(server.io_processed));
+
+ if (listLength(server.io_newjobs)) {
+ redisLog(REDIS_DEBUG,"[P] There are new jobs, signal");
+ pthread_cond_signal(&server.io_condvar);
+ }
+#endif
+
+ /* Check if we can process some finished job */
io_processed_len = listLength(server.io_processed);
+ redisLog(REDIS_DEBUG,"[P] Unblock IO");
unlockThreadedIO();
+ redisLog(REDIS_DEBUG,"[P] Wait");
+ usleep(10000);
if (io_processed_len) {
vmThreadedIOCompletedJob(NULL,server.io_ready_pipe_read,
(void*)0xdeadbeef,0);
- usleep(1000); /* 1 millisecond */
- } else {
- usleep(10000); /* 10 milliseconds */
+ processed++;
+ if (max != -1) max--;
}
}
+ return processed;
+}
+
+void waitEmptyIOJobsQueue(void) {
+ processActiveIOJobs(-1);
}
-void vmReopenSwapFile(void) {
- /* Note: we don't close the old one as we are in the child process
- * and don't want to mess at all with the original file object. */
- server.vm_fp = fopen(server.vm_swap_file,"r+b");
- if (server.vm_fp == NULL) {
- redisLog(REDIS_WARNING,"Can't re-open the VM swap file: %s. Exiting.",
- server.vm_swap_file);
- _exit(1);
+/* Process up to 'max' IO Jobs already completed by threads but still waiting
+ * processing from the main thread.
+ *
+ * If max == -1 all the pending jobs are processed.
+ *
+ * The number of processed jobs is returned. */
+int processPendingIOJobs(int max) {
+ int processed = 0;
+
+ while(max == -1 || max > 0) {
+ int io_processed_len;
+
+ lockThreadedIO();
+ io_processed_len = listLength(server.io_processed);
+ unlockThreadedIO();
+ if (io_processed_len == 0) break;
+ vmThreadedIOCompletedJob(NULL,server.io_ready_pipe_read,
+ (void*)0xdeadbeef,0);
+ if (max != -1) max--;
+ processed++;
}
- server.vm_fd = fileno(server.vm_fp);
+ return processed;
+}
+
+void processAllPendingIOJobs(void) {
+ processPendingIOJobs(-1);
}
/* This function must be called while with threaded IO locked */
spawnIOThread();
}
-int vmSwapObjectThreaded(robj *key, robj *val, redisDb *db) {
+/* Consume all the IO scheduled operations, and all the thread IO jobs
+ * so that eventually the state of diskstore is a point-in-time snapshot.
+ *
+ * This is useful when we need to BGSAVE with diskstore enabled. */
+void cacheForcePointInTime(void) {
+ redisLog(REDIS_NOTICE,"Diskstore: synching on disk to reach point-in-time state.");
+ while (listLength(server.cache_io_queue) != 0) {
+ cacheScheduleIOPushJobs(REDIS_IO_ASAP);
+ processActiveIOJobs(1);
+ }
+ waitEmptyIOJobsQueue();
+ processAllPendingIOJobs();
+}
+
+void cacheCreateIOJob(int type, redisDb *db, robj *key, robj *val, time_t expire) {
iojob *j;
j = zmalloc(sizeof(*j));
- j->type = REDIS_IOJOB_PREPARE_SWAP;
+ j->type = type;
j->db = db;
j->key = key;
incrRefCount(key);
- j->id = j->val = val;
- incrRefCount(val);
- j->canceled = 0;
- j->thread = (pthread_t) -1;
- val->storage = REDIS_VM_SWAPPING;
+ j->val = val;
+ if (val) incrRefCount(val);
+ j->expire = expire;
lockThreadedIO();
queueIOJob(j);
+ pthread_cond_signal(&server.io_condvar);
unlockThreadedIO();
- return REDIS_OK;
}
-/* ============ Virtual Memory - Blocking clients on missing keys =========== */
+/* ============= Disk store cache - Scheduling of IO operations =============
+ *
+ * We use a queue and an hash table to hold the state of IO operations
+ * so that's fast to lookup if there is already an IO operation in queue
+ * for a given key.
+ *
+ * There are two types of IO operations for a given key:
+ * REDIS_IO_LOAD and REDIS_IO_SAVE.
+ *
+ * The function cacheScheduleIO() function pushes the specified IO operation
+ * in the queue, but avoid adding the same key for the same operation
+ * multiple times, thanks to the associated hash table.
+ *
+ * We take a set of flags per every key, so when the scheduled IO operation
+ * gets moved from the scheduled queue to the actual IO Jobs queue that
+ * is processed by the IO thread, we flag it as IO_LOADINPROG or
+ * IO_SAVEINPROG.
+ *
+ * So for every given key we always know if there is some IO operation
+ * scheduled, or in progress, for this key.
+ *
+ * NOTE: all this is very important in order to guarantee correctness of
+ * the Disk Store Cache. Jobs are always queued here. Load jobs are
+ * queued at the head for faster execution only in the case there is not
+ * already a write operation of some kind for this job.
+ *
+ * So we have ordering, but can do exceptions when there are no already
+ * operations for a given key. Also when we need to block load a given
+ * key, for an immediate lookup operation, we can check if the key can
+ * be accessed synchronously without race conditions (no IN PROGRESS
+ * operations for this key), otherwise we blocking wait for completion. */
+
+#define REDIS_IO_LOAD 1
+#define REDIS_IO_SAVE 2
+#define REDIS_IO_LOADINPROG 4
+#define REDIS_IO_SAVEINPROG 8
+
+void cacheScheduleIOAddFlag(redisDb *db, robj *key, long flag) {
+ struct dictEntry *de = dictFind(db->io_queued,key);
+
+ if (!de) {
+ dictAdd(db->io_queued,key,(void*)flag);
+ incrRefCount(key);
+ return;
+ } else {
+ long flags = (long) dictGetEntryVal(de);
+
+ if (flags & flag) {
+ redisLog(REDIS_WARNING,"Adding the same flag again: was: %ld, addede: %ld",flags,flag);
+ redisAssert(!(flags & flag));
+ }
+ flags |= flag;
+ dictGetEntryVal(de) = (void*) flags;
+ }
+}
+
+void cacheScheduleIODelFlag(redisDb *db, robj *key, long flag) {
+ struct dictEntry *de = dictFind(db->io_queued,key);
+ long flags;
+
+ redisAssert(de != NULL);
+ flags = (long) dictGetEntryVal(de);
+ redisAssert(flags & flag);
+ flags &= ~flag;
+ if (flags == 0) {
+ dictDelete(db->io_queued,key);
+ } else {
+ dictGetEntryVal(de) = (void*) flags;
+ }
+}
+
+int cacheScheduleIOGetFlags(redisDb *db, robj *key) {
+ struct dictEntry *de = dictFind(db->io_queued,key);
+
+ return (de == NULL) ? 0 : ((long) dictGetEntryVal(de));
+}
+
+void cacheScheduleIO(redisDb *db, robj *key, int type) {
+ ioop *op;
+ long flags;
+
+ if ((flags = cacheScheduleIOGetFlags(db,key)) & type) return;
+
+ redisLog(REDIS_DEBUG,"Scheduling key %s for %s",
+ key->ptr, type == REDIS_IO_LOAD ? "loading" : "saving");
+ cacheScheduleIOAddFlag(db,key,type);
+ op = zmalloc(sizeof(*op));
+ op->type = type;
+ op->db = db;
+ op->key = key;
+ incrRefCount(key);
+ op->ctime = time(NULL);
+
+ /* Give priority to load operations if there are no save already
+ * in queue for the same key. */
+ if (type == REDIS_IO_LOAD && !(flags & REDIS_IO_SAVE)) {
+ listAddNodeHead(server.cache_io_queue, op);
+ cacheScheduleIOPushJobs(REDIS_IO_ONLYLOADS);
+ } else {
+ /* FIXME: probably when this happens we want to at least move
+ * the write job about this queue on top, and set the creation time
+ * to a value that will force processing ASAP. */
+ listAddNodeTail(server.cache_io_queue, op);
+ }
+}
+
+/* Push scheduled IO operations into IO Jobs that the IO thread can process.
+ *
+ * If flags include REDIS_IO_ONLYLOADS only load jobs are processed:this is
+ * useful since it's safe to push LOAD IO jobs from any place of the code, while
+ * SAVE io jobs should never be pushed while we are processing a command
+ * (not protected by lookupKey() that will block on keys in IO_SAVEINPROG
+ * state.
+ *
+ * The REDIS_IO_ASAP flag tells the function to don't wait for the IO job
+ * scheduled completion time, but just do the operation ASAP. This is useful
+ * when we need to reclaim memory from the IO queue.
+ */
+#define MAX_IO_JOBS_QUEUE 10
+int cacheScheduleIOPushJobs(int flags) {
+ time_t now = time(NULL);
+ listNode *ln;
+ int jobs, topush = 0, pushed = 0;
+
+ /* Don't push new jobs if there is a threaded BGSAVE in progress. */
+ if (server.bgsavethread != (pthread_t) -1) return 0;
+
+ /* Sync stuff on disk, but only if we have less
+ * than MAX_IO_JOBS_QUEUE IO jobs. */
+ lockThreadedIO();
+ jobs = listLength(server.io_newjobs);
+ unlockThreadedIO();
+
+ topush = MAX_IO_JOBS_QUEUE-jobs;
+ if (topush < 0) topush = 0;
+ if (topush > (signed)listLength(server.cache_io_queue))
+ topush = listLength(server.cache_io_queue);
+
+ while((ln = listFirst(server.cache_io_queue)) != NULL) {
+ ioop *op = ln->value;
+ struct dictEntry *de;
+ robj *val;
+
+ if (!topush) break;
+ topush--;
+
+ if (op->type != REDIS_IO_LOAD && flags & REDIS_IO_ONLYLOADS) break;
+
+ /* Don't execute SAVE before the scheduled time for completion */
+ if (op->type == REDIS_IO_SAVE && !(flags & REDIS_IO_ASAP) &&
+ (now - op->ctime) < server.cache_flush_delay) break;
+
+ /* Don't add a SAVE job in the IO thread queue if there is already
+ * a save in progress for the same key. */
+ if (op->type == REDIS_IO_SAVE &&
+ cacheScheduleIOGetFlags(op->db,op->key) & REDIS_IO_SAVEINPROG)
+ {
+ /* Move the operation at the end of the list if there
+ * are other operations, so we can try to process the next one.
+ * Otherwise break, nothing to do here. */
+ if (listLength(server.cache_io_queue) > 1) {
+ listDelNode(server.cache_io_queue,ln);
+ listAddNodeTail(server.cache_io_queue,op);
+ continue;
+ } else {
+ break;
+ }
+ }
+
+ redisLog(REDIS_DEBUG,"Creating IO %s Job for key %s",
+ op->type == REDIS_IO_LOAD ? "load" : "save", op->key->ptr);
+
+ if (op->type == REDIS_IO_LOAD) {
+ cacheCreateIOJob(REDIS_IOJOB_LOAD,op->db,op->key,NULL,0);
+ } else {
+ time_t expire = -1;
+
+ /* Lookup the key, in order to put the current value in the IO
+ * Job. Otherwise if the key does not exists we schedule a disk
+ * store delete operation, setting the value to NULL. */
+ de = dictFind(op->db->dict,op->key->ptr);
+ if (de) {
+ val = dictGetEntryVal(de);
+ expire = getExpire(op->db,op->key);
+ } else {
+ /* Setting the value to NULL tells the IO thread to delete
+ * the key on disk. */
+ val = NULL;
+ }
+ cacheCreateIOJob(REDIS_IOJOB_SAVE,op->db,op->key,val,expire);
+ }
+ /* Mark the operation as in progress. */
+ cacheScheduleIODelFlag(op->db,op->key,op->type);
+ cacheScheduleIOAddFlag(op->db,op->key,
+ (op->type == REDIS_IO_LOAD) ? REDIS_IO_LOADINPROG :
+ REDIS_IO_SAVEINPROG);
+ /* Finally remove the operation from the queue.
+ * But we'll have trace of it in the hash table. */
+ listDelNode(server.cache_io_queue,ln);
+ decrRefCount(op->key);
+ zfree(op);
+ pushed++;
+ }
+ return pushed;
+}
+
+void cacheCron(void) {
+ /* Push jobs */
+ cacheScheduleIOPushJobs(0);
+
+ /* Reclaim memory from the object cache */
+ while (server.ds_enabled && zmalloc_used_memory() >
+ server.cache_max_memory)
+ {
+ int done = 0;
+
+ if (cacheFreeOneEntry() == REDIS_OK) done++;
+ if (negativeCacheEvictOneEntry() == REDIS_OK) done++;
+ if (done == 0) break; /* nothing more to free */
+ }
+}
+
+/* ========== Disk store cache - Blocking clients on missing keys =========== */
/* This function makes the clinet 'c' waiting for the key 'key' to be loaded.
- * If there is not already a job loading the key, it is craeted.
- * The key is added to the io_keys list in the client structure, and also
+ * If the key is already in memory we don't need to block.
+ *
+ * FIXME: we should try if it's actually better to suspend the client
+ * accessing an object that is being saved, and awake it only when
+ * the saving was completed.
+ *
+ * Otherwise if the key is not in memory, we block the client and start
+ * an IO Job to load it:
+ *
+ * the key is added to the io_keys list in the client structure, and also
* in the hash table mapping swapped keys to waiting clients, that is,
* server.io_waited_keys. */
int waitForSwappedKey(redisClient *c, robj *key) {
struct dictEntry *de;
- robj *o;
list *l;
- /* If the key does not exist or is already in RAM we don't need to
- * block the client at all. */
+ /* Return ASAP if the key is in memory */
de = dictFind(c->db->dict,key->ptr);
- if (de == NULL) return 0;
- o = dictGetEntryVal(de);
- if (o->storage == REDIS_VM_MEMORY) {
- return 0;
- } else if (o->storage == REDIS_VM_SWAPPING) {
- /* We were swapping the key, undo it! */
- vmCancelThreadedIOJob(o);
- return 0;
- }
+ if (de != NULL) return 0;
- /* OK: the key is either swapped, or being loaded just now. */
+ /* Don't wait for keys we are sure are not on disk either */
+ if (!cacheKeyMayExist(c->db,key)) return 0;
/* Add the key to the list of keys this client is waiting for.
* This maps clients to keys they are waiting for. */
listAddNodeTail(l,c);
/* Are we already loading the key from disk? If not create a job */
- if (o->storage == REDIS_VM_SWAPPED) {
- iojob *j;
- vmpointer *vp = (vmpointer*)o;
-
- o->storage = REDIS_VM_LOADING;
- j = zmalloc(sizeof(*j));
- j->type = REDIS_IOJOB_LOAD;
- j->db = c->db;
- j->id = (robj*)vp;
- j->key = key;
- incrRefCount(key);
- j->page = vp->page;
- j->val = NULL;
- j->canceled = 0;
- j->thread = (pthread_t) -1;
- lockThreadedIO();
- queueIOJob(j);
- unlockThreadedIO();
- }
+ if (de == NULL)
+ cacheScheduleIO(c->db,key,REDIS_IO_LOAD);
return 1;
}
if (listLength(c->io_keys)) {
c->flags |= REDIS_IO_WAIT;
aeDeleteFileEvent(server.el,c->fd,AE_READABLE);
- server.vm_blocked_clients++;
+ server.cache_blocked_clients++;
return 1;
} else {
return 0;
projects / redis.git / blobdiff